Câu hỏi của Nguyễn Tiến Đạt

Question

giúp mình 2 câu này với

Đoàn Đức Hà · Accepted Answer

2) $A=3+3^2+3^3+...+3^{12}$$3A=3^2+3^3+3^4+...+3^{13}$$3A-A=\left(3^2+3^3+3^4+...+3^{13}\right)-\left(3+3^2+3^3+...+3^{12}\right)$$2A=3^{13}-3$$A=\frac{3^{13}-3}{2}$Suy ra $3^{13}=3^x\Leftrightarrow x=13$.$x+2016=13+2016=2029$3) $A=5.4^{15}.9^9-4.3^{20}.8^9=5.2^{30}.3^{18}-3^{20}.2^{29}=2^{29}.3^{18}\left(5.2-3^2\right)=2^{29}.3^{18}$$B=5.2^9.6^{19}-7.2^{29}.27^6=5.2^{28}.3^{19}-7.2^{29}.3^{18}=2^{28}.3^{18}\left(5.3-7.2\right)=2^{28}.3^{18}$$\frac{A}{B}=\frac{2^{29}.3^{18}}{2^{28}.3^{18}}=2$Câu trả lời: 2) $A=3+3^2+3^3+...+3^{12}$$3A=3^2+3^3+3^4+...+3^{13}$$3A-A=\left(3^2+3^3+3^4+...+3^{13}\right)-\left(3+3^2+3^3+...+3^{12}\right)$$2A=3^{13}-3$$A=\frac{3^{13}-3}{2}$Suy ra $3^{13}=3^x\Leftrightarrow x=13$.$x+2016=13+2016=2029$3) $A=5.4^{15}.9^9-4.3^{20}.8^9=5.2^{30}.3^{18}-3^{20}.2^{29}=2^{29}.3^{18}\left(5.2-3^2\right)=2^{29}.3^{18}$$B=5.2^9.6^{19}-7.2^{29}.27^6=5.2^{28}.3^{19}-7.2^{29}.3^{18}=2^{28}.3^{18}\left(5.3-7.2\right)=2^{28}.3^{18}$$\frac{A}{B}=\frac{2^{29}.3^{18}}{2^{28}.3^{18}}=2$

BukiBi · Answer

2) A = 3 + 3^2 + 3^3 + ... + 3^12 = 3^x-3/2 3A = 3^2 + 3^3 + ... + 3^13 . 2A = 3A - A = 3^13 - 3 => x =13. Vậy x + 2016 = 20293) A= 5 . 2^30 . 3^18 - 3^20 . 2^29 = 2^29 . 3^18 . (5.2 - 3^2) = 2^29 . 3^18B = 5. 2^28 . 3^19 - 7.2^29. 3^18 = 2^28.3^18 . ( 5.3 - 7.2 ) = 2^28.3^18A/B = 2^29 . 3^18 / 2^28 . 3^18 = 2Câu trả lời: 2) A = 3 + 3^2 + 3^3 + ... + 3^12 = 3^x-3/2 3A = 3^2 + 3^3 + ... + 3^13 . 2A = 3A - A = 3^13 - 3 => x =13. Vậy x + 2016 = 20293) A= 5 . 2^30 . 3^18 - 3^20 . 2^29 = 2^29 . 3^18 . (5.2 - 3^2) = 2^29 . 3^18B = 5. 2^28 . 3^19 - 7.2^29. 3^18 = 2^28.3^18 . ( 5.3 - 7.2 ) = 2^28.3^18A/B = 2^29 . 3^18 / 2^28 . 3^18 = 2

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